Datasheet
MAX3480A/MAX3480B
Complete, Isolated, 3.3V
RS-485/RS-422 Data Interface
10 ______________________________________________________________________________________
shutdown circuitry that puts the driver outputs into a
high-impedance state. The receiver input has a fail-safe
feature that guarantees a logic-high output if the input
is open circuit.
The driver outputs are enabled by bringing DE´ high.
Driver-enable times are typically 200ns for the
MAX3480A and 50µs for the MAX3480B. Allow time for
the devices to be enabled before sending data. When
enabled, driver outputs function as line drivers. Driver
outputs are high impedance when DE´ is low. While
outputs are high impedance, they function as line
receivers.
The MAX3480A/MAX3480B typically withstand
1600V
RMS
(1 minute) or 2000V
RMS
(1 second). The iso-
lated outputs of these devices meet all RS-485/RS-422
specifications. The logic inputs can be driven from any
TTL/CMOS-logic family with a series resistor, and the
received data output can directly drive any of the
TTL/CMOS-logic families with only a resistive pull-up.
Boost Voltage
The MAX3480 requires external diodes on the primary
of the transformer to develop the boost voltage for the
power oscillator. In normal operation, whenever one of
the oscillator outputs (D1 and D2) goes low, the other
Figure 2. Typical Application Circuit
AC1 (MAKE NO CONNECTION)
AC2 (MAKE NO CONNECTION)
SHIELD (OPTIONAL)
EXTERNAL RS-485/RS-422 WIRING
ISO V
CC1
B
D2
D1
D1, D2
1N914
V
CC2
V
CC1
ISO RO DRV
A
B
A
SH
ISO DI IN
ISO DE IN
V
CC3
SD
FS
GND1
ISO COM1
ISO DI DRV
ISO V
CC2
ISO DE DRV
GND2
DE
V
CC4
DI
ISO COM2
ISO RO LED
V
CC5
RO
R
L
R
L
R4
R5
R1
R2
16
14
12
5
7
13
15
18
3
8 2
DI
DE
RO
17
20
9
10
11 RECEIVER OUTPUT
6
4
R8
100
C3
0.01µF
R6
200Ω
R7
R3
BOOSTED V+
74HC240
DRIVER INPUT
DRIVER ENABLE
V
IN
3.0V TO 3.6V
22µF
6V
0.1µF
C1 C2
MAX3480A/B
LOGIC GROUND
ISOLATION BARRIER
ISOLATION COMMON
MAX485
MAX487
MAX845
1
2
28
27
3
4
5
6
7
8
9
10
11
12
13
14
26
25
24
23
22
21
20
19
18
17
16
15
SHIELD (OPTIONAL)
NOTE: RESISTOR R8 PROTECTS
THE MAX3480 FROM TRANSIENT
CURRENTS BETWEEN SHIELD AND
“A” & “B”.
TWISTED PAIR
TO OTHER TRANSCEIVERS
TERMINATING RESISTOR
(ONE RESISTOR ON EACH END)
TWISTED PAIR
TO OTHER TRANSCEIVERS
Table 1. Pull-Up and LED Drive Resistors
PART R1 (Ω) R2 (Ω) R3 (Ω) R4 (Ω) R5 (Ω) R6 (Ω)
MAX3480A 150 130 680 3000 1000 200
MAX3480B 130 330 2000 2200 3000 200
R7 (Ω)
Open
470